We present the results of a Hubble Space Telescope (HST) study of dwarf
galaxies in the outer regions of the nearby rich Perseus cluster, down
to MV=-12, and compare these with the dwarf population in the
cluster core from our previous HST imaging. In this paper, we examine
how properties such as the colour-magnitude relation, structure and
morphology are affected by environment for the lowest mass galaxies.
Dwarf galaxies are excellent tracers of the effects of environment due
to their low masses, allowing us to derive their environmentally based
evolution, which is more subtle in more massive galaxies. We identify 11
dwarf elliptical (dE) and dwarf spheroidal (dSph) galaxies in the outer
regions of Perseus, all of which are previously unstudied. We measure
the (V-I)0 colours of our newly discovered dEs, and find that
these dwarfs lie on the same red sequence as those in the cluster core.
The morphologies of these dwarfs are examined by quantifying their light
distributions using concentration, asymmetry and clumpiness (CAS)
parameters, and we find that dEs in the cluster outskirts are on average
more disturbed than those in the core, with = 0.13 ±
0.09 and = 0.18 ± 0.08, compared to = 0.02
± 0.04, = 0.01 ± 0.07 for those in the core.
Based on these results, we infer that these objects are `transition
dwarfs', likely in the process of transforming from late-type to
early-type galaxies as they infall into the cluster, with their colours
transforming before their structures. When we compare the number counts
for both the core and outer regions of the cluster, we find that below
MV=-12, the counts in the outer regions of the cluster exceed
those in the core. This is evidence that in the very dense region of the
cluster, dwarfs are unable to survive unless they are sufficiently
massive to prevent their disruption by the cluster potential and
interactions with other galaxies. Based on observations made with the
NASA/ESA HST, obtained (from the Data Archive) at the Space Telescope
Science Institute, which is operated by the Association of Universities
for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These
observations are associated with programs GO-10201 and GO-10789